1. Field of the Invention
This invention relates to springs, and more particularly concerns polymer springs.
2. Description of the Prior Art
Polymer springs are used for a wide variety of applications. For instance, applications vary from use with diving boards to uses in truck mounts, shock absorbers, and railroad car cushioning units.
One type of polymer spring is the straight cylinder polymer spring 11, which, as shown in FIGS. 1 and 2, has a cylindrical body 13 having a cylindrical axial bore 15 extending through it. Upon application of sufficient compressive force on this type of spring 11, the central portion 17 of the spring 11 bulges outwardly, as shown in FIGS. 3a, 3b, and 3c, creating stress points in the spring 11 at its bulged portion, which may lead to failure of the spring 11 due to the spring ripping or tearing typically somewhere at or near the portion of the spring 11 that has bulged outwardly the most. Further, upon application of sufficient compressive force on the spring 11, in addition to the stress on the central portion 17 of the spring 11 when the central portion 17 of the spring 11 bulges outwardly, additional stress areas on the spring 11 are created, as shown by reference number 19 and 20 shown in FIGS. 3a to 3c, where the bulged central portion 17 of the spring 11 meets the remainder of the spring 11 above and below the bulged central portion 17. Too much stress at these high stress areas 19 and 20 may cause the spring 11 to fail due to the spring tearing or ripping at these high stress areas 19 and 20. Moreover, the spring 11 may fail if the force on the spring 11 causes the spring 11 to buckle or fold, as illustrated in FIGS. 4a to 4c, when the central portion 17 of the spring 11 has bulged outwardly. Additionally, once the spring folds or buckles, its spring load capacity is permanently reduced due to permanent loss in the height of the spring due to material fatigue at the buckling or folding point.
Another type of polymer spring is the pre-bulged spring 21, shown in FIGS. 5a to 5c, which is formed such that in a non-compressed state (that is, prior to force being applied to the spring 21 when the spring 21 is in use), the central portion 27 of the spring 21 already is bulged outwardly. Like the straight cylindrical spring 11 shown in FIGS. 1 and 2, upon application of sufficient force on the pre-bulged spring 21, high stress areas 29 and 30 are formed on the pre-bulged spring 21 where the bulged central portion 27 of the pre-bulged spring 21 meets the remainder of the pre-bulged spring 21 above and below its bulged portion 27, which may lead to the pre-bulged spring 21 tearing or ripping at these high stress areas 29 and 30 if too much stress is incurred. Further, the pre-bulged spring 21 may fail if the force on the pre-bulged spring 21 causes the spring 21 to buckle on fold at its central portion 27, as illustrated in FIGS. 6a to 6c. Additionally, once the spring folds or buckles, its spring load capacity is permanently reduced due to permanent loss in the height of the spring due to material fatigue at the buckling or folding point.
Another type of polymer spring is the constrained spring 31, such as that shown in FIGS. 7a, 7b and 8, which is similar to the straight cylinder spring 11, except it is provided with a washer 32 around its periphery. Upon application of sufficient compressive force on this type of spring 31, outward bulging of the spring 31 occurs above and below the washer 32, as illustrated in FIGS. 9a and 9b, creating stress points in the spring 31 at its bulged portions 37, which may lead to failure of the spring 31 due to the spring 31 ripping or tearing typically somewhere at or near the portions of the spring 31 that have bulged outwardly the most. Further, upon application of sufficient compressive force on the spring 31, in addition to stress on the bulged portions 37, additional stress areas on the spring 31 are created, as shown by reference numbers 39 and 40, in the body 33 of the spring 31 at each end of the bulged portions 37, as well as in the body 33 of the spring 31 at the washer 32. Too much stress at these stress areas, including high stress areas 39 and 40, may cause the spring 31 to fail due to the spring 31 tearing or ripping at these high stress areas. Moreover, the spring 31 may fail if the force on the spring 31 causes the spring 31 to buckle or fold, as illustrated in FIGS. 10a and 10b, in the bulged portions 37. Additionally, once the spring folds or buckles, its spring load capacity is permanently reduced due to permanent loss in the height of the spring due to material fatigue at the buckling or folding point.